One of the things we learned when trying to match up the dialog to facial expressions were to keep the sound of the whole word in mind, rather than breaking it down into individual letters or syllables. Also, it's best to skim over the words so that you can avoid having the characters mouths opening and closing constantly.
One of the problems I had with my lip sync was that the dialog is spoken very quickly, and the words tended to blend in to each other. A handy function to have would have been if you had been able to hear audio playback when you flick between frames, but I couldn't find a function like that.
One technique that I sort of discovered on my own though, was forming the mouth shapes before the dialog occurred. All I did to achieve this was shift all the frames forward on the timeline. For example, I formed the mouth shapes for the word 'beautiful' about five frames ahead of when we actually hear the dialog.
Then I found this tutorial online that backed up that technique, and also showed me that you don't always need a lot of mouth movements to create a good lip-sync. You only really need to mimic the main vowel sounds.
I think that it doesn't work so well on my lip-sync because my character's face isn't moving (only his mouth), so it makes it more noticeable. Oh well, lesson learned!